This invention relates generally to the sharpening of cutting edges of tools, such as knives and arrow heads, and more particularly to a hand held sharpening device for such tools. The invention can sharpen both single and double-sided blades.
As long as mankind has utilized sharpened devices and cutting instruments such as knives and blades there has been a need for methods and devices for keeping those devices sharp.
Many sharpening devices have been proposed over the years, utilizing a wide variety of sharpening blade shapes and sharpening angles. Some sharpeners utilize round sharpening blades, such as U.S. Pat. No. 4,112,790 to Marder, and U.S. Pat. No. 5,377,563 to Weeks. Due to the radial nature of the sharpening blades these devices do not provide a true xe2x80x9cVxe2x80x9d shaped edge to the sharpened device, and therefore do not achieve the best shape or durability for the sharpened workpiece.
Other devices rely upon abrasive-type sharpening elements, such as U.S. Pat. No. 4,530,188 to Graves. However, due to the inherently inexact nature of the shape of the sharpening elements, and in particular as extended use wear causes the shape to change, these type of devices also are unable to ensure that the optimal xe2x80x9cVxe2x80x9d shaped edge results.
Sharpeners have been proposed that utilize beveled metallic sharpening elements, in a variety of shapes. For triangular elements, see U.S. Pat. No. 4,599,919 to Fortenberry, and U.S. Pat. No. 562,223 to Hausse. For square elements, see U.S. Pat. No. 584,933 to Friedrich. While previously proposed devices of this type can obtain the desired xe2x80x9cVxe2x80x9d shaped edge, they do not precisely position the sharpening elements to provide the best degree of angle to the sharpened edge. And while some allow the sharpening elements to be rotated or exchanged to provide fresh sharpening edges, they do not increase the sharpener element utilization. They also do not increase the useful life of the sharpening elements.
According to the present invention a sharpening tool is provided which comprises a body with recesses for detachably holding sharpening elements. The recesses are shaped to hold the sharpening elements in a fixed position with respect to each other so that the angle of intersection of the elements is a precise fixed value, thereby ensuring a fixed value for the resultant sharpened workpiece edge shape. Preferably the sharpening elements have sharpening edges which have a point of coincidence with respect to each other located along the sharpening edges between their midpoints and one of their ends, so that exchanging and rotating the detachable elements results in each sharpening edge of each element providing two distinct sharpening points, doubling the useful life of the edges as compared to previously proposed sharpeners. The elements are also spaced so that they do not contact each other while sharpening a work piece; this prevents the elements from vibrating against each other while sharpening a work piece, and therefore prevents vibration related cracking and chipping of the elements. Preferably a removable, adjustable handguard is also provided.
The invention is also adaptable to sharpen a single-sided or single-edged cutting blade. This type of blade has a cutting edged formed by beveling on one side of the cutting element. Examples are common household scissors, and cutting shears. The invention is adapted by replacing a sharpening element with a non-sharpening xe2x80x9crestxe2x80x9d for receiving the side of the blade opposite the beveled side.